Methods and compositions for the repair of articular cartilage defects in mammals

ABSTRACT

Provided are methods and compositions for the repair of articular cartilage defects in a mammal. Denuded chondrogenic cells are proliferated ex vivo as monolayer cultures in order to expand the pool of available chondrogenic cells. During proliferation the chondrogenic cells stop secreting the extracellular matrix components, type II collagen and sulfated proteoglycans. The proliferated cells then are seeded into a pre-shaped well having a cell contacting, cell abhesive surface. The cells cultured in the well redifferentiate and begin to secrete cartilage-specific extracellular matrix again. Accordingly, essentially unlimited amounts of synthetic cartilage may be prepared from small samples of biopsy tissue. Also provided are methods for surgically repairing articular cartilage defects in mammals using the synthetic cartilage prepared in accordance with the invention.

This is a divisional application Ser. No. 08/245,565 filed on May 5,1994, now abandoned.

FIELD OF THE INVENTION

This invention relates to methods and compositions for the repair ofarticular cartilage defects in a mammal. The methods and syntheticcartilage compositions of the invention are particularly useful intreatment of partial-thickness and full-thickness articular cartilagedefects.

BACKGROUND OF THE INVENTION

Cartilage is a hyperhydrated structure with water comprising 70% to 80%of its weight. The remaining 20% to 30% comprises type II collagen andproteoglycan. The collagen usually accounts for 70% of the dry weight ofcartilage (in "Pathology" (1988) Eds. Rubin & Farber, J. B. LippincottCompany, PA. pp. 1369-1371). Proteoglycans are composed of a centralprotein core from which long chains of polysaccharides extend. Thesepolysaccharides, called glycosaminoglycans, include:chondroitin-4-sulfate; chondroitin-6-sulfate; and keratan sulfate.Cartilage has a characteristic structural organization consisting ofchondrogenic cells dispersed within an endogenously produced andsecreted extracellular matrix. The cavities in the matrix which containthe chondrocytes are called cartilage lacunae. Unlike bone, cartilage isneither innervated nor penetrated by either the vascular or lymphaticsystems (Clemente (1984) in "Gray's Anatomy, 30^(th) Edit," Lea &Febiger).

Three types of cartilage are present in a mammal and include: hyalinecartilage; fibrocartilage and elastic cartilage (Rubin and Farber,supra). Hyaline cartilage consists of a gristly mass having a firm,elastic consistency, is translucent and is pearly blue in color. Hyalinecartilage is predominantly found on the articulating surfaces ofarticulating joints. It is found also in epiphyseal plates, costalcartilage, tracheal cartilage, bronchial cartilage and nasal cartilage.Fibrocartilage is essentially the same as hyaline cartilage except thatit contains fibrils of type I collagen that add tensile strength to thecartilage. The collagenous fibers are arranged in bundles, with thecartilage cells located between the bundles. Fibrocartilage is foundcommonly in the anulus fibrosus of the invertebral disc, tendinous andligamentous insertions, menisci, the symphysis pubis, and insertions ofjoint capsules. Elastic cartilage also is similar to hyaline cartilageexcept that it contains fibers of elastin. It is more opaque thanhyaline cartilage and is more flexible and pliant. These characteristicsare defined in part by the elastic fibers embedded in the cartilagematrix. Typically, elastic cartilage is present in the pinna of theears, the epiglottis, and the larynx.

The surfaces of articulating bones in mammalian joints are covered witharticular cartilage. The articular cartilage direct contact of theopposing bone surfaces and the near frictionless movement of thearticulating bones relative to one another (Clemente, supra).

Two types of articular cartilage defects are commonly observed inmammals and include full-thickness and partial-thickness defects. Thetwo-types of defects differ not only in the extent of physical damagebut also in the nature of repair response each type of lesion elicits.

Full-thickness articular cartilage defects include damage to thearticular cartilage, the underlying subchondral bone tissue, and thecalcified layer of cartilage located between the articular cartilage andthe subchondral bone. Full-thickness defects typically arise duringsevere trauma of the joint or during the late stages of degenerativejoint diseases, for example, during osteoarthritis. Since thesubchondral bone tissue is both innervated and vascularized, damage tothis tissue is often painful. The repair reaction induced by damage tothe subchondral bone usually results in the formation of fibrocartilageat the site of the full-thickness defect. Fibrocartilage, however, lacksthe biomechanical properties of articular cartilage and fails to persistin the joint on a long term basis.

Partial-thickness articular cartilage defects are restricted to thecartilage tissue itself. These defects usually include fissures orclefts in the articulating surface of the cartilage. Partial-thicknessdefects are caused by mechanical derangements of the joint which in turninduce wearing of the cartilage tissue within the joint. In the absenceof innervation and vasculature, partial-thickness defects do not elicitrepair responses and therefore tend not to heal. Although painless,partial-thickness defects often degenerate into full-thickness defects.

Repair of articular cartilage defects with suspensions of isolatedchondrocytes has been attempted in a variety of animal models. See forexample: Bentley, et al. (1971) Nature 230:385-388; Langer et al. (1974)J. Bone Joint Surg. 56-A:297-304; Green (1977) Clin. Orthop.124:237-250; and Aston et al. (1986) J. Bone Joint Surg. 68-B:29-35).During transplantation, the cell suspensions may be retained in thedefect behind a piece of periosteal tissue that has been previouslyattached to the surface of the normal cartilage tissue. The rate ofsuccessful implantation using cell suspensions was found to be about40%. It is believed that chondrocytes transplanted in this manner losetheir viability during transplantation and that the procedure may resultin the formation of fibrocartilage or islands of cartilage embedded infibrous tissue at the site of the defect.

Three alternative approaches have been developed in an attempt toimprove the success rate in treating mammalian articular cartilagedefects. In the first approach, synthetic carrier matrices containingdispersed allogeneic chondrocytes may be implanted into the cartilagedefect. The implanted chondrocytes hopefully produce and secretecomponents of the extracellular matrix thereby to form articularcartilage at the site of the defect in situ. In the second approach,synthetic carrier matrices containing chemotactic and mitogenic growthfactors may be implanted into the cartilage defect. The growth factorshopefully induce the influx into, and the proliferation of chondrocyteprogenitor cells within the matrix. The chondrocyte progenitor cellsdifferentiate subsequently into chondrocytes that in turn secretecomponents of the extracellular matrix thereby to form articularcartilage at the site of the defect in situ. In the third approach,synthetic cartilage tissue may be grown in vitro and implantedsubsequently into the cartilage defect.

In the first approach, the synthetic matrices or biological resorbableimmobilization vehicles may be impregnated with allogeneic chondrocytes.A variety of synthetic carrier matrices have been used to date andinclude: three-dimensional collagen gels (U.S. Pat. No. 4,846,835;Nishimoto (1990) Med. J. Kinki University 15; 75-86; Nixon et al. (1993)Am. J. Vet. Res. 54:349-356; Wakitani et al. (1989) J. Bone Joint Surg.71B:74-80; Yasui (1989) J. Jpn. Ortho. Assoc. 63:529-538); reconstitutedfibrin-thrombin gels (U.S. Pat. Nos. 4,642,120; 5,053,050 and4,904,259); synthetic polymer matrices containing polyanhydride,polyorthoester, polyglycolic acid and copolymers thereof (U.S. Pat. No.5,041,138); and hyaluronic acid-based polymers (Robinson et al. (1990)Calcif. Tissue Int. 46:246-253).

The introduction of non-autologous materials into a patient, however,may stimulate an undesirable immune response directed against theimplanted material. Such an immune response has been observed in rabbitmodels (Yoshinao (1990) J. Jpn. Orth. Assoc. 64:835-846. In addition,there is evidence to suggest that neo-cartilage may be formed around theperiphery of the implant thereby preventing integration of the implantinto the cartilage defect. See for example, Messner (1994) 40^(th)Annual Meeting Orth. Res. Soc., New Orleans p. 239; and Nixon et al.(1994) 40^(th) Annual Meeting Orth. Res. Soc., New Orleans p. 241.Monitoring the formation and development of the resulting syntheticcartilage in situ can be difficult to perform and usually involves anarthroscopic or open joint examination. Furthermore, implants containingsynthetic polymer components may be unsuitable for repairing largecartilage defects since polymer hydrolysis in situ may inhibit theformation of cartilage and/or its integration into the defect.

In the second approach, the defect may be filled with a biocompatible,biodegradable matrix containing growth factors to stimulate the influxof chondrocyte progenitor cells into the matrix in situ. The matricesoptimally contain pores of sufficient dimensions to permit the influxinto, and proliferation of the chondrocyte progenitor within the matrix.The matrix also may contain differentiating growth factors to stimulatethe differentiation of chondrocyte progenitor cells into chondrocytes.The resulting chondrocytes hopefully secrete extracellular matrixcomponents thereby to form cartilage at the site of the defect in situ.See for example, U.S. Pat. Nos. 5,206,023; 5,270,300; and EP 05 30 804A1. This approach, however, may have problems similar to thoseassociated with the first approach, hereinabove.

In the third approach, chondrocytes may be cultured in vitro thereby toform synthetic cartilage-like material. The resulting cartilage may beimplanted subsequently into the cartilage defect. This type of approachhas the advantage over the previous methods in that the development ofthe synthetic cartilage material may be monitored prior to implantation.In addition, the resulting cartilage may be characterized biochemicallyand morphologically prior to implantation. Two general procedures havebeen developed for growing synthetic cartilage in vitro. These includegrowing chondrogenic cells in either an anchorage-dependent or ananchorage-independent manner.

In the anchorage-independent manner, the chondrogenic cells may becultured as colonies within an agarose gel. See for example: Benya etal. (1982) Cell 30:215-224; Aydlotte et al. (1990) in Methods andCartilage Research Chapter 23:pp. 90-92; Aulthouse et al. (1989) InVitro Cellular and Developmental Biology 25:659-668; Delbruck et al.(1986) Connective Tissue Res. 15:1550-172; and Bohme et al. (1992) J.Cell Biol. 116:1035-1042. Heretofore, only small pieces of cartilagetissue of undefined shape have been prepared using this approach.Furthermore, the resulting cartilage remains embedded within a gelmatrix making it unsuitable for implantation into mammals.Alternatively, in another anchorage-independent method, chondrocytes maybe cultured as colonies in suspension culture. See for example,Franchimont et al. (1989) J. Rheumatol. 16:5-9; and Bassleer et al.(1990) in "Methods and Cartilage Research", Academic Press Ltd., Chapter24. As with the gel approach, the resulting particles containingsynthethic cartilage-like material may be small and of undefined shapethus making the particles unsuitable for implantation and repair of apredetermined articular cartilage defect.

In the anchorage-dependent method, primary cultures of chondrogeniccells isolated from primary tissue may be grown as monolayers attachedto the surface of a cell culture flask. See for example: Yoshihashi(1983) J. Jpn. Ortho. Assoc. 58:629-641; and U.S. Pat. No. 4,356,261.The primary cells derived directly from explant tissue remain capable ofproducing and secreting extracellular components characteristic ofnatural cartilage, specifically, type II collagen and sulfatedproteoglycans. However, it was observed that after passaging andproliferating the cells as monolayers, by serially passaging the cells,the cells dedifferentiate and lose their ability to secrete type IIcollagen and sulfated proteoglycans (Schlitz et al., (1973) CellDifferentiation 1:97-108; Mayne et al. (1975) Proc. Natl. Acad. Sci. USA72:4511-4515; Mayne et al. (1976) Proc. Natl. Acad. Sci. USA73:1674-1678; Okayama et al. (1976) Proc. Natl. Acad. Sci. USA73:3224-3228; Pacifici & Holtzer (1977) Am. J. Anat. 150:207-212;Pacifici et al. (1977) Cell 11:891-899; West et al. (1979) Cell17:491-501; von der Mark (1980) Curr. Top. Dev. Biol. 14:199-225; Oegamaand Thompson (1981) J. Biol. Chem. 256:1015-1022; Benya & Schaffer,supra). Consequently, until now it has not been possible to preparelarge patches of articular cartilage from small pieces of biopsy tissueusing the anchorage-dependent procedures disclosed in U.S. Pat. No.4,356,261 and Yoshihashi (supra) since the chondrocytes, following theproliferation as monolayers, dedifferentiate and stop secreting acartilage-specific extracellular matrix.

It is an object of the invention to provide a variety of methods andcompositions for the repair of articular cartilage defects in a mammal.Specifically, it is an object of the invention to provide a method forpreparing in vitro large quantities of synthetic cartilage from smallsamples of biopsy tissue for the repair of articular cartilage defectsin a mammal. The proliferated but undifferentiated chondrogenic cellsmay be cultured under conditions that stimulate the secretion ofextracellular components characteristic of cartilage. Another object isto provide a method for producing a patch of synthetic cartilage ofpredetermined volume in vitro. Yet another object is to providemethodologies for preparing synthetic cartilage from chondrocytesisolated from a variety of tissues including pre-existing cartilagetissue and perichondrial tissue. Still another object is to providemethodologies for the repair of articular cartilage defects in a mammalusing the compositions described herein.

These and other objects and features of the invention will be apparentfrom the description, drawings, and claims which follow.

SUMMARY OF THE INVENTION

It has been discovered that large quantities of three-dimensional, multicell-layered synthetic cartilage may be prepared in vitro from smallbiopsy samples by the practice of the invention described herein. Also,it has been discovered that synthetic cartilage patches ofpre-determined volume may be prepared in vitro by culturing chondrogeniccells in an anchorage-independent manner in a pre-shaped well.Furthermore, it has been discovered that chondrogenic cells useful inthe practice of the instant invention may be isolated from a variety oftissues, for example: pre-existing cartilage; perichondrial tissue; orbone marrow, and expanded in vitro prior to cartilage formation. Thesediscoveries enable the preparation of patches of synthetic cartilage forthe repair of articular cartilage defects in a mammalian joint.

Broadly, the invention comprises a method for preparing in vitro asynthetic cartilage patch for the repair of a cartilage defect in amammal. The method includes: (1) seeding denuded chondrogenic cells,proliferated ex vivo, into a pre-shaped well having a cell contacting,cell abhesive surface; and (2) culturing the proliferated chondrogeniccells in the well for a time sufficient to permit the cells to secretean extracellular matrix thereby to form a three-dimensional, multicell-layered patch of synthetic cartilage. The resulting syntheticcartilage, preferably synthetic articular cartilage, containschondrogenic cells dispersed within an endogenously produced andsecreted extracellular matrix. The resulting synthetic cartilage patchmay be used subsequently for the repair of an articular cartilage defectin a mammal.

As used herein, the term "synthetic cartilage", is understood to meanany cartilage tissue produced in vitro that contains chondrogenic cellsdispersed within an endogenously produced and secreted extracellularmatrix. The extracellular matrix is composed of collagen fibrils(predominantly fibrils of type II collagen), sulfated proteoglycans, forexample, chondroitin-6-sulfate and keratan sulfate, and water.

As used herein, the term "synthetic articular cartilage", is understoodto mean any cartilage tissue produced in vitro that biochemically andmorphologically resembles the cartilage normally found on thearticulating surfaces of mammalian joints.

As used herein, the term "chondrogenic cell", is understood to mean anycell which, when exposed to an appropriate stimuli, may differentiateinto a cell capable of producing and secreting components characteristicof cartilage tissue, for example, fibrils of type II collagen, and thesulfated proteoglycans, chondroitin-6-sulfate and keratan sulfate.

As used herein, the term "denuded cell" is understood to mean any cellthat has been isolated from a disaggregated tissue containing such acell. The tissue of interest may be enzymatically and/or mechanicallydisaggregated in order to release the denuded cells.

As mentioned hereinabove, the cells are cultured in a pre-shaped wellhaving a cell contacting, cell abhesive surface. The cell abhesivesurface discourages the chondrogenic cells from attaching to the cellcontacting surface of the well. The use of such a well having a cellcontacting, cell abhesive surface is a critical aspect of the instantinvention. Heretofore, it has been observed that chondrogenic cellsexpanded by serially passaging the cells as monolayers usually losetheir ability to secrete type II collagen and sulfated proteoglycans. Itnow has been discovered that the undifferentiated, proliferatedchondrogenic cells when cultured in such a well redifferentiate and onceagain start to secrete cartilage specific type II collagen and sulfatedproteoglycans.

It is contemplated that the actual dimensions of the well may bepre-determined when the actual size and shape of the cartilage defect tobe repaired is known. For example, the well may be dimensioned such thatthe resulting cartilage may interfit directly into the cartilage defect.Alternatively, the synthetic cartilage patch may be "trimmed"mechanically to the appropriate size and shape by the surgeon prior toinsertion into the defect during a surgical procedure. It is appreciatedthat synthetic cartilage patches prepared in such a manner have theadditional advantage over patches prepared as anchorage-dependentprimary explant cultures in that the patches may be easily removed fromthe well obviating the use of enzymatic or other mechanical procedures.Such procedures may affect deleteriously the biochemical and/orbiomechanical properties of the resulting cartilage patch.

Cell abhesive surfaces may be prepared by coating the cell contactingsurface of a well with a reagent that discourages cell attachment.Preferred reagents include, but are not limited to, silicon basedreagents, for example, dichlorodimethylsilane or polytetrafluoroethylenebased reagents, for example, Teflon®. Alternatively, the well may becast in a material that naturally discourages the attachment ofchondrogenic cells. Preferred materials include, but are not limited to,agarose, glass, untreated cell culture plastic andpolytetrafluoroethylene, for example, Teflon®. It is contemplated thatany biocompatible material or coating capable of discouraging theattachment of chondrogenic cells may be useful in the practice of theinstant invention.

Chondrogenic cells useful in the practice of the invention may beisolated from essentially any tissue containing chondrogenic cells. Forexample, the chondrogenic cells may be isolated directly frompre-existing cartilage tissue, for example, hyaline cartilage, elasticcartilage, or fibrocartilage. Specifically, chondrogenic cells may beisolated from articular cartilage (from either weight bearing ornon-weight bearing joints), costal cartilage, nasal cartilage, auricularcartilage, tracheal cartilage, epiglottic cartilage, thyroid cartilage,arytenoid cartilage and cricoid cartilage. Methods for isolatingchondrogenic cells from such tissues are set forth hereinbelow.Alternatively, chondrogenic cells may be isolated from bone marrow. Seefor example, U.S. Pat. Nos. 5,197,985 and 4,642,120, and Wakitani et al.(1994) J. Bone Joint Surg. 76:579-591, the disclosures of which areincorporated by reference herein.

Once chondrogenic cells have been isolated from the pre-existing tissuethey are proliferated ex vivo in monolayer culture using conventionaltechniques well known in the art. See for example, Pollack (1975) in"Readings in Mammalian Cell Culture", Cold Spring Harbor LaboratoryPress, Cold Spring Harbor, the disclosure of which is incorporated byreference herein. Briefly, the population of chondrogenic cells isexpanded by culturing the cells as monolayers and by serially passagingthe cells. The chondrogenic cells are passaged after the cells haveproliferated to such a density that they contact one another on thesurface of the cell culture plate. During the passaging step, the cellsare released from the substratum. This is performed routinely by pouringa solution containing a proteolytic enzyme, i.e, trypsin, onto themonolayer. The proteolytic enzyme hydrolyzes proteins which anchor thecells on the substratum. As a result, the cells are released from thesurface of the substratum. The resulting cells, now in suspension, arediluted with culture medium and replated into a new tissue culture dishat a cell density such that the cells do not contact one another. Thecells subsequently reattach onto the surface of the tissue culture andstart to proliferate once again. Alternatively, the cells in suspensionmay be cryopreserved for subsequent use using techniques well known inthe art. See for example, Pollack (supra).

The cells are repeatedly passaged until enough cells have beenpropagated to prepare a piece of synthetic cartilage of pre-determinedsize. As a result, a population containing a small number ofchondrogenic cells originally isolated from a biopsy sample may beexpanded in vitro thereby to generate a large number of chondrogeniccells for subsequent use in the practice of the invention.

Following proliferative expansion, the chondrogenic cells areenzymatically released from the substratum to provide a suspension ofcells. The cells in suspension then are diluted by the addition of cellculture medium to give a cell density of about 1×10⁵ -1×⁹ proliferatedchondrogenic cells per ml, or more preferably about 1×10⁶ -5×10⁸ cellsper ml, and most preferably about 3×10⁶ -2×10⁸ cells per ml. The cellsthen are seeded into the pre-shaped well having a cell contacting, cellabhesive surface. About, 1×10³ -1×10⁷ cells, preferably 1×10⁴ -1×10⁶cells, and most preferably about 5×10⁴ -5×10⁵ cells produce a piece ofsynthetic cartilage 1 mm³ in volume. Accordingly, the artisan mayproduce a patch of synthetic cartilage of pre-determined size by seedingan appropriate number of chondrogenic cells into a pre-shaped well. Thecells subsequently are cultured in the well under conventional cellculture conditions well known in the art from 1 to 90 days, preferably 5to 60 days, and most preferably 10 to 30 days thereby to induce theproduction and secretion of extracellular matrix. The present inventiontherefore enables the production of large quantities of syntheticcartilage patches from small pieces of biopsied tissue.

In a preferred embodiment, the chondrogenic cells, once proliferated exvivo, may be seeded into a preshaped well dimensioned to determine thevolume of the resulting cartilage tissue. Therefore, using themethodologies described herein, one skilled in the art may preparesynthetic cartilage of pre-determined volume for the repair of articularcartilage defects of pre-determined volume.

In another preferred embodiment, polypeptide growth factors may be addedto the chondrogenic cells in the pre-shaped well to enhance or stimulatethe production of cartilage specific proteoglycans and/or collagen.Preferred growth factors include, but are not limited to, transforminggrowth factor-β (TGF-β), insulin-like growth factor (IGF), plateletderived growth factor (PDGF), epidermal growth factor (EGF), acidic orbasic fibroblast growth factor (aFBF or bFBF), hepatocytic growth factor(HGF), keratinocyte growth factor (KGF) the bone morphogenic factors(BMPs) including: BMP-1; BMP-2; BMP-3; BMP-4; BMP-5; and BMP-6 and theosteogenic proteins (OPs) including: OP-1; OP-2; and OP-3. In addition,it is contemplated that ascorbate may be added to the chondrogenic cellsin the pre-shaped well to enhance or stimulate the production ofcartilage specific proteoglycans and collagen. However, these particularcompounds are not limiting. Any compound or composition capable ofstimulating or inducing the production of cartilage specificproteoglycans and collagen may be useful in the practice of the instantinvention.

The invention also provides methodologies for effecting the re of anarticular cartilage at a pre-determined site in a mammal. The methodcomprises the steps of: (1) surgically implanting at the pre-determinedsite a piece of synthetic cartilage prepared by the methodologiesdescribed herein; and (2) permitting the synthetic cartilage tointegrate into the pre-determined site. The synthetic cartilage patchmay be fixed in place during the surgical procedure. This may beeffected by surgically fixing the patch with sutures and/or by applyinga biocompatible, bioadhesive to the surface interfacing the cartilagepatch and the defect. In some instances, defective cartilage tissue maybe removed prior to implantation. Although the shape of the syntheticcartilage may be dimensioned to interfit with the cartilage defect, inspecific instances, for example, when the defect is large, it iscontemplated that a plurality of synthetic cartilage patches may besurgically implanted into the defect.

In another preferred embodiment, the resulting synthetic cartilage patchis preferably allogenic, and more preferably autogenic in nature.Accordingly, synthetic allogenic cartilage may be prepared from biopsytissue isolated from a mammal belonging to the same species as therecipient. Synthetic autogenic cartilage may be prepared from biopsytissue derived from the intended recipient. In another preferredembodiment, the invention provides synthetic articular cartilage for therepair articular cartilage defects in humans. Accordingly, chondrogeniccells may be isolated from human cartilage tissue,i.e., human articularcartilage (from weight bearing and non-weight bearing joints), humancostal cartilage, human nasal cartilage, human auricular cartilage,human tracheal cartilage, human epiglottic cartilage, human thyroidcartilage, human arytenoid-cartilage and human cricoid cartilage.Alternatively, the chondrogenic cells useful in the practice of theinvention may be derived from human bone marrow.

The methodologies described herein are useful in the treatment of bothpartial-thickness and full-thickness defects of articular cartilage.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and features of the invention, as wellas the invention itself, may be more fully understood from the followingdescription, when read together with the accompanying drawings, inwhich:

FIG. 1 shows a flow chart summarizing the steps in the preparation oflarge amounts of synthetic cartilage from small samples of biopsy tissuefor the repair of cartilage defects in a mammal. Initially, tissuecontaining chondrogenic cells is disaggregated to release denudedchondrogenic cells. The isolated, cells then are proliferated byserially culturing and passaging the cells in monolayer culture. Duringmonolayer culture the chondrogenic cells dedifferentiate and lose theirability to secrete cartilage specific extracellular matrix. Once theappropriate number of cells have been obtained, the proliferated cellsare seeded into a pre-shaped well having a cell contacting, cellabhesive surface. The chondrogenic cells are cultured in the well for atime sufficient to allow them to redifferentiate and secrete a cartilagespecific extracellular matrix thereby to form synthetic cartilage invitro.

FIGS. 2a and 2b provide a schematic plan view and a cross-sectionalillustration, respectively, of a patch of synthetic cartilage preparedin a pre-shaped well in accordance with the invention.

DETAIL DESCRIPTION OF THE INVENTION

It has been discovered that chondrogenic cells sampled from a mammal andproliferated in monolayer culture ex vivo may be cultured further in apre-shaped well having a cell contacting, cell abhesive surface therebyto generate a three-dimensional, multi cell-layered patch of syntheticcartilage. In addition, it has been discovered that synthetic cartilagepatches of pre-determined volume for use in the surgical replacement ofdamaged articular cartilage and subsequent integration into the joint ofthe recipient may be prepared in accordance with the invention. Also, ithas been discovered that chondrogenic cells useful in the practice ofthe instant invention may be isolated from a variety of pre-existingtissues, for example, cartilage tissue and perichondrial tissue oralternatively from bone marrow. These discoveries enable preparation ofpotentially unlimited quantities of synthetic cartilage patches ofpre-determined thickness or volume and thus provides a significantadvance in the repair of articular cartilage defects in a mammal.

A flow chart summarizing the steps associated with the preparation ofthree-dimensional, multi cell-layered patches of synthetic cartilage isshown in FIG. 1. All of the steps described hereinbelow are preferablyperformed under aseptic conditions.

Briefly, tissue (10) containing chondrogenic cells (12) is disaggregatedto release denuded chondrogenic cells (16) from their extracellularmatrix (14). The denuded cells then are isolated and proliferated asmonolayers in an undifferentiated state ex vivo (18). The passagingprocedure may be repeated multiple times (n), for example up to about 7to 10 passages until enough cells have been propagated to prepare apiece of cartilage of pre-determined size. These steps expand the numberof chondrogenic cells in a population that can be used subsequently toform the three-dimensional, multi cell-layered patch of syntheticcartilage.

The proliferated but undifferentiated chondrogenic cells (20) then areseeded into a pre-shaped well (24) having a cell contacting, cellabhesive surface (22). The cell abhesive surface prevents chondrogeniccells cultured in the well from attaching to the surface of the well.The cells, deprived of anchorage, interact with one another and coalescewithin hours to generate a cohesive plug of cells. The chondrogeniccells then begin to differentiate, as characterized by the productionand secretion of cartilage-specific markers, i.e., type II collagen andsulfated proteoglycans. Type II collagen is found specifically incartilage. The chondrogenic cells then are cultured in the well for timesufficient to permit the formation of a three-dimensional, multicell-layered patch of synthetic cartilage (26). The resulting syntheticcartilage patch comprises chondrogenic cells (20) dispersed with a new,endogenously produced and secreted extracellular matrix (28). Theextracellular matrix deposited during this procedure is biochemicallyand morphologically similar to the extracellular matrix found in naturalcartilage. Specifically, the synthetic matrix comprises fibers of typeII collagen, and sulfated proteoglycans such as chondroitin sulfate andkeratan sulfate.

FIG. 2a is a schematic top plan view of a patch of synthetic cartilage(26) prepared in a pre-shaped well (24) in accordance with theinvention. FIG. 2b is a schematic cross-sectional view of the patch ofcartilage in the well of FIG. 1 taken at lines 2-2. Particulars ofmethods for making and using the synthetic cartilage are set forth indetail below.

I. Isolation of Tissue Containing Chondrogenic Cells

Chondrogenic cells useful in the practice of the instant invention maybe sampled from a variety of sources in a mammal that contain suchcells, for example, pre-existing cartilage tissue, perichondrial tissueor bone marrow.

Although costal cartilage, nasal cartilage, auricular cartilage,tracheal cartilage, epiglottic cartilage, thyroid cartilage, arytenoidcartilage and cricoid cartilage are useful sources of chondrogeniccells, articular cartilage (from either weight bearing or non-weightbearing joints) is the preferred source. Biopsy samples of articularcartilage may be readily isolated by a surgeon performing arthroscopicor open joint surgery. Procedures for isolating biopsy tissues are wellknown in the art and so are not described in detailed herein. See forexample, "Operative Arthroscopy" (1991) by McGinty et al.,; Raven Press,New York, the disclosure of which is incorporated by reference herein.

Perichondrial tissue is the membranous tissue that coats the surface ofall types of cartilage, except for articular cartilage. Perichondrialtissue provides nutrients to the chondrocytes located in the underlyingunvascularized cartilage tissue. Perichondrial tissue sampled fromcostal (rib) cartilage of patients suffering from osteoporosis providesa source of chondrogenic cells when the normal articular cartilage isdiseased or unavailable. Biopsy samples of perichondrial tissue may beisolated from the surface of costal cartilage or alternatively from thesurface of auricular cartilage, nasal cartilage and cricoid cartilageusing simple surgical procedures well known in the art. See for example:Skoog et al. (1990) Scan. J. Plast. Reconstr. Hand Surg. 24:89-93;Bulstra et al. (1990) J. Orthro. Res. 8:328-335; and Homminga et al.(1990) J. Bone Constr. Surg. 72:1003-1007, the disclosures of which areincorporated by reference herein.

It is contemplated also that chondrogenic cells, specificallymesenchymal cells, useful in the practice of the invention may beisolated from bone marrow. Surgical procedures useful in the isolationof bone marrow are well known in the art and so are not described indetailed herein. See for example, Wakitani et al. (1994) J. Bone JointSurg. 76: 579-591, the disclosure of which is incorporated by referenceherein.

II. Preparation of Denuded Chondrogenic Cells

Protocols for preparing denuded chondrogenic cells from cartilagetissue, perichondrial tissue, and bone marrow are set forth below.

A. From Articular Cartilage

Articular cartilage, both loaded (weight bearing) and unloaded(non-weight bearing), maybe be subjected to enzymatic treatment in orderto disaggregate the tissue and release denuded chondrogenic cells fromthe extracellular matrix. Solutions containing proteolytic enzymes, forexample, chondroitinase ABC, hyaluronidase, pronase, collagense, ortrypsin may be added to articular cartilage tissue in order to digestthe extracellular matrix. See for example, Watt & Dudhia (1988)Differentiation 38:140-147, the disclosure of which is incorporatedherein by reference.

In a preferred procedure, articular cartilage is initially cut intopieces of about 1 mm in diameter, or less. This is routinely performedusing a sterile scalpel. The minced tissue then is disaggregatedenzymatically, for example, by the addition of a solution containing0.1% collagenase (Boehringer Mannheim GmbH, Germany). Approximately 1 mlof collagenase is added per 0.25 ml equivalents of minced tissue. Thesample is then mixed and incubated overnight (up to 16 hours) at 37° C.,with agitation. Following the overnight digestion, the residual piecesof tissue are harvested by centrifugation, the supernatant removed, andthe remaining cartilage pieces redigested by the addition of a solutioncontaining, for example, 0.25% collagenase and 0.05% trypsin (SigmaChemical Co., St. Louis). Approximately 1 ml of 0.25% collagenase, 0.05%trypsin is added per 0.25 ml equivalents of residual tissue. The samplethen is mixed and incubated for 2-4 hours at 37° C., with agitation. Anyremaining tissue is pelleted by centrifugation and the cell suspensionharvested. The collagenase, trypsin step is repeated 2-4 times or untilthe tissue is completely disaggregated.

The enzymatic reaction is terminated by the addition of tissue culturemedium supplemented with approximately 10% fetal bovine serum (FBS)(Hyclone, Logan, Utah). A preferred cell culture medium includes, forexample, Dulbecco's minimal essential medium (DMEM) (Sigma Chemical Co.,St. Louis) supplemented with 10% FBS. An alternative cell culture mediumincludes a 1:1 (vol/vol) mixture of Medium 199 (Sigma Chemical Co., St.Louis) and Molecular Cell Developmental Biology Medium 202 (MCDB 202)(Sigma Chemical Co., St. Louis), respectively, supplemented with 10%FBS. Alternatively, another cell culture medium useful in the practiceof the invention includes a 3:1 (vol/vol) mixture of DMEM and Ham's F-12(F12) (Sigma Chemical Co., St. Louis), respectively, supplemented with10% FBS. Fractions containing denuded chondrogenic cells are combined,and the cells inoculated into a cell culture dish at a plating densityof about 1×10² -5×10⁵ cells/cm², preferably about 5×10² -1×10⁵cells/cm², and most preferably about 1×10³ -1×10⁴ cells/cm², for cellexpansion and testing.

Chondrocytes may be isolated from costal cartilage, nasal cartilage,auricular cartilage, tracheal cartilage, epiglottic cartilage, thyroidcartilage, arytenoid cartilage and cricoid cartilage using theaforementioned procedure.

B. From Perichondrial Tissue

Denuded chondrogenic cells preferably are isolated from perichondrialtissue using the same procedure as described in section II A,hereinabove.

Briefly, the tissue is minced into pieces of about 1 mm in diameter, orless. The minced tissue is repeatedly digested with proteolytic enzymes,for example, trypsin and collagenase. The resulting denuded cells areinoculated into a cell culture dish at a plating density of about 1×10²-5×10⁵ cells/cm², preferably about 5×10² to 1×10⁵ cells/cm², and mostpreferably about 1×10³ -1×10⁴ cells/cm² for cell expansion and testing.

Alternatively, a non-destructive procedure may be used to isolatechondrogenic cells from perichondrial tissue. In this procedure, intactexplant tissue is placed in a cell culture dish and incubated in growthmedium. The chondrogenic cells located within the tissue migrate out ofthe tissue and onto the surface of the tissue plate where they begin toproliferate. See for example, Bulstra et al. (1990) J. Orthop. Res.8:328-335, the disclosure of which is incorporated by reference herein.Briefly, pieces of the minced explant tissue are placed into a tissueculture plate containing tissue culture medium. A preferred cell culturemedium comprises DMEM supplemented with 10% FBS. The explant tissues areincubated at 37° C., 5% CO₂ for 3-7 days. During this time thechondrogenic cells migrate out of the explant tissue and onto thesurface of the tissue culture dish. After reattaching to the surface ofthe plate, the cells start to proliferate again.

C. From Bone Marrow

Chondrogenic cells, specifically mesenchymal cells, may be isolated fromsamples of bone marrow. Procedures useful for the isolation ofmesenchymal cells from bone marrow are well known in the art, see forexample: U.S. Pat. Nos. 5,197,985; 4,642,120; and Wakitani et al. (1994,supra).

For example, in a preferred method, a plug of bone marrow may be removedsurgically from the mammal of interest and added to cell culture medium.Preferred complete growth media are disclosed in U.S. Pat. No.5,197,985. The mixture then is vortexed to break up the plug of tissue.The resulting suspension is centrifuged to separate bone marrow cellsfrom large pieces of particulate matter i.e., bone fragments. The cellsthen are dissociated to give a single cell suspension by forcing thecells through a syringe fitted with a series of 16, 18, and 20 gaugeneedles. The cells then are plated out into a tissue culture plate at acell density of about 1×10⁵ -1×10⁶ cells/cm² for selectively separatingand/or isolating bone marrow derived mesenchymal cells from theremaining cells present in the suspension.

III. Expansion of Denuded Chondrogenic Cells In Vitro Chondrogenic cellsisolated from cartilage tissue, perichondrial tissue, or bone marrowusing the methods described in section II hereinabove may be placed inmonolayer culture for proliferative expansion. The process enables oneto amplify the number of isolated chondrogenic cells. In principal, theartisan may produce essentially an unlimited number of chondrogeniccells and therefore essentially an unlimited amount of syntheticcartilage. It is appreciated, however, that during proliferativeexpansion the chondrogenic cells dedifferentiate and lose their abilityto secrete cartilage specific extracellular matrix. A procedure to assaywhether the undifferentiated cells still retain their chondrogenicpotential is described hereinbelow.

A. Cell Proliferation

Protocols for proliferating cells by monolayer culture are well known inthe art, see for example, Pollack (supra), and so are not described indetail herein.

Briefly, monolayer cultures are initiated by inoculating primarychondrogenic cells, isolated from either cartilage tissue orperichondrial tissue, into a cell culture dish at a plating densitydensity of about 1×10² -5×10⁵ cells/cm², more preferably about 5×10²-1×10⁵ cells/cm² and most preferably about 1×10³ -1×10⁴ cells/cm².Chondrogenic cells that have undergone one or more cycles of passagingare also plated out at the same plating densities. Primary chondrogeniccells isolated from bone marrow are plated out into a tissue cultureplate at a cell density of about 1×10⁵ -1×10⁶ cells/cm². Chondrogeniccells from bone marrow that have undergone one or more cycles ofpassaging are plated out at plating densities of about 1×10² -5×10⁵cells/cm², more preferably about 5×10² -1×10⁵ cells/cm² and mostpreferably about 1×10³ -1×10⁴ cells/cm². The chondrogenic cellssubsequently are cultured at 37° C., 5% CO₂ in cell culture medium.

A preferred cell culture medium comprises DMEM supplemented with 10%FBS. Alternatively, a cell culture medium comprising a 1:1 (vol/vol)mixture of Medium 199 and MCDB 202, respectively, supplemented with 10%FBS may be used. Still another cell culture medium useful in thepractice of the invention comprises a 3:1 (vol/vol) mixture of DMEM andF12, respectively, supplemented with 10% FBS.

Once the cell cultures become confluent, i.e., the cells grow to such adensity on the surface of the plate that they contact one another, thecells are passaged and inoculated into a new plate. This may beaccomplished by initially removing the cell culture medium overlayingthe cells monolayer by aspiration, and washing the cell monolayer withphosphate buffered saline (PBS). The PBS is removed, by aspiration, anda solution containing a proteolytic enzyme, i.e., 0.1% trypsin, then ispoured onto the monolayer. The proteolytic enzyme hydrolyzes proteinsthat anchor the cells onto the surface of the plate thereby releasingthe cells from the surface of the plate. The proteolytic enzyme in thecell suspension then is inactivated by adding FBS to the suspension togive a final concentration of 10% (vol/vol). The density of cells in thesuspension then is estimated and the cells re-plated into a new cellculture plate at a density of about 1×10² -5×10⁵ cells, more preferablyabout 5×10² -1×10⁵ cells, and most preferably about 1×10³ -10⁴ cells percm². The passaging procedure may be repeated multiple times, for exampleup to about 7 to 10 times, until enough cells have been propagated toprepare a piece of cartilage of pre-determined size.

It is appreciated that suspensions of proliferated cells may becryopreserved indefinitely using techniques well known in the art. Seefor example, Pollack (supra). Accordingly, populations of chondrogeniccells may be stored for subsequent use whenever a necessity arises.

B. Assay To Measure Chondrogenic Potential of Proliferated Cells

Undifferentiated chondrogenic cells, expanded in monolayer culture, maybe assayed to determine whether they still retain their chondrogenicpotential. This may be performed by culturing the cells in a semi-solidmedium in a process called agarose culture. This procedure is describedin Benya et al. (1982) Cell 30:215-224, the disclosure of which isincorporated by reference herein.

Briefly, proliferated chondrogenic cells are seeded into a solution ofwarm 2% low melting temperature agarose (LT agarose) (BioRad, Richmond,Calif.). The use of LT agarose permits cells to be seeded into theagarose without thermal damage to the cells. The agarose is cooled toabout 39°-41° C. prior to the addition of cells. Approximately 1×10³-1×10⁶ cells are seeded into 1 ml of the liquid agarose.

The cells are cultured subsequently at 37° C., 5% CO₂ for 3-4 weeks in acell culture medium preferably containing DMEM supplemented with 10%FBS. During this time, the chondrogenic cells replicate to from colonieswhich start to secrete an extracellular matrix. The resulting colonieshave the appearance of small "nodules" embedded within the agarose. Thecolonies may be counted and the chondrogenic proportion of cellsdetermined histochemically and immunohistochemically using procedureswell known in the art.

Histochemical Staining

Briefly, agarose gels containing the cells are fixed with 10% formalinin PBS. The samples then are sectioned into 8-18 μm sections with acryo-cut microtome (American Optical). General cellular morphology andtissue phenotype may be assessed by staining the section by thehematoxylin-eosin method well known in the art. Briefly, the resultingsection is incubated in a stain comprising hematoxylin dissolved in 5%ethanol for 10 minutes. The section then is washed with water andincubated subsequently in an stain containing 1% eosin in 70% ethanolfor 45 seconds. The sections then are washed with 95% ethanol. Thenodules of extracellular matrix stain purple under these experimentalconditions.

Sulfated proteoglycans in the extracellular matrix may be visualized byincubating the agarose particles in a stain comprising 1% alcian blue in0.1N hydrochloric acid for 15-30 minutes. Alternatively, proteoglycansmay be visualized by incubating the agarose particles in a staincomprising 0.2% safranin O/fast green in 1% acetic acid for 15-30minutes. The stained particles then are washed with water. Sulfatedproteoglycans present in the extracellular matrix stain blue and orange,by the two methods, respectively.

Immunohistochemical Staining

The agarose particles containing the chondrogenic cells are sectionedinto 8-18 μm sections with a cryo-cut microtome (American Optical). Thesections then are enzymatically digested in order to expose antigenicepitopes present on the extracellular matrix. A preferred enzymeincludes the proteolytic enzyme protease type XIV (Sigma Chemical Co.,St. Louis). Briefly, the agarose sections are incubated for 90 minutesat room temperature in Tris buffered saline, pH 7.4 (TBS) containing 0.4mg/ml of protease type XIV. The resulting section then is washed twicewith TBS.

Monoclonal antibodies that bind: link protein (8A4 from Hybridoma Bank,Baltimore, Md.); type I collagen (AB745 and MAB1340 from ChemiconInternational, Timacula, Calif.); type II collagen (PS48 from SanBioInc., Amsterdam, Holland; CIICI from Hybridoma Bank, Baltimore, Md.);and chondroitin-6-sulfate (MabCs-D from Seikagaku America Inc,Rockville, Md.) may be used to detect the presence of theseextracellular components in the agarose particles. Immunostaining may beperformed using the VECTASTAIN ABC-AP kit (Vector Laboratory) pursuantto the manufacturers instructions.

IV. Preparation of Synthetic Cartilage Patch

Following proliferation, the chondrogenic cells still havingchondrogenic potential are cultured in an anchorage-independent manner,i.e., in a well having a cell contacting, cell abhesive surface, inorder to stimulate the secretion of cartilage-specific extracellularmatrix components.

Heretofore, it has been observed that chondrogenic cells proliferativelyexpanded in an anchorage-dependent manner usually dedifferentiate andlose their ability to secrete cartilage-specific type II collagen andsulfated proteoglycan (Schlitz et al., supra; Mayne et al., supra; Mayneet al., supra; Okayama et al., supra; Pacifici & Holtzer, supra;Pacifici et al., supra; West et al., supra; von der Mark, supra; Oegama& Thompson, supra; Benya & Schaffer, supra). It has been discovered anddisclosed herein that undifferentiated chondrogenic cells, when seededinto, and cultured in a well having a cell contacting surface thatdiscourages adhesion of cells to the cell contacting surface,redifferentiate and start to secrete cartilage-specific collagen andsulfated proteoglycans thereby to form a patch of synthetic cartilage invitro.

In addition, it has been found that culturing the cells in a pre-shapedwell, enables one to manufacture synthetic cartilage patches ofpre-determined thickness and volume. It is appreciated, however, thatthe volume of the resulting patch of cartilage is dependent not onlyupon the volume of the well but also upon the number of chondrogeniccells seeded into the well. Cartilage of optimal pre-determined volumemay be prepared by routine experimentation by altering either, or bothof the aforementioned parameters.

A. Preparation of Pre-shaped Well

Several approaches are available for preparing pre-shaped wells withcell contacting, cell abhesive surfaces.

The cell contacting surface of the well may be coated with a moleculethat discourages adhesion of chondrogenic cells to the cell contactingsurface. Preferred coating reagents include silicon based reagents i.e.,dichlorodimethylsilane or polytetrafluoroethylene based reagents, i.e.,Teflon®. Procedures for coating materials with silicon based reagents,specifically dichlorodimethylsilane, are well known in the art. See forexample, Sambrook et al. (1989) "Molecular Cloning A Laboratory Manual",Cold Spring Harbor Laboratory Press, the disclosure of which isincorporated by reference herein. It is appreciated that otherbiocompatible reagents that prevent the attachment of cells to thesurface of the well may be useful in the practice of the instantinvention.

Alternatively, the well may be cast from a pliable or moldablebiocompatible material that does not permit attachment of cells per se.Preferred materials that prevent such cell attachment include, but arenot limited to, agarose, glass, untreated cell culture plastic andpolytetrafluoroethylene, i.e., Teflon®. Untreated cell culture plastics,i.e., plastics that have not been treated with or made from materialsthat have an electrostatic charge are commercially available, and may bepurchased, for example, from Falcon Labware, Becton-Dickinson, LincolnPark, N.J. The aforementioned materials, however, are not meant to belimiting. It is appreciated that any other other pliable or moldablebiocompatible material that inherently discourages the attachment ofchondrogenic cells may be useful in the practice of the instantinvention.

The size and shape of the well may be determined by the size and shapeof the articular cartilage defect to be repaired. For example, it iscontemplated that the well may have a cross-sectional surface area of 25cm². This is the average cross-sectional surface area of an adult, humanfemoral chondyle. Accordingly, it is anticipated that a single piece ofsynthetic cartilage may be prepared in accordance with the invention inorder to resurface the entire femoral chondyle. The depth of the well ispreferably greater than about 0.3 cm and preferably about 0.6 cm indepth. The thickness of natural articular cartilage in an adultarticulating joint is usually about 0.3 cm. Accordingly, the depth ofthe well should be large enough to permit a cartilage patch of about 0.3cm to form. However, the well should also be deep enough to containgrowth medium overlaying the cartilage patch.

It is contemplated also that a large piece of cartilage prepared inaccordance with the invention may be "trimmed" to a pre-selected sizeand shape by a surgeon performing surgical repair of the damagedcartilage. Trimming may be performed with the use of a sharp cuttingimplement, i.e., a scalpel, a pair of scissors or an arthroscopic devicefitted with a cutting edge, using procedures well known in the art.

The pre-shaped well preferably is cast in a block of agarose gel underaseptic conditions. Agarose is an economical, biocompatible, pliable andmoldable material that can be used to cast pre-shaped wells, quickly andeasily. As mentioned above, the dimensions of the well may dependentupon the size of the resulting cartilage plug that is desired.

A pre-shaped well may be prepared by pouring a hot solution of molten LTagarose (BioRad, Richmond, Calif.) into a tissue culture dish containinga cylinder. The cylinder having dimensions that mirror the shape of thewell to be formed. The size and shape of the well may be chosen by theartisan and may be dependent upon the shape of the articular cartilagedefect to be repaired. Once the agarose has cooled and solidified aroundthe cylinder, the cylinder is carefully removed with forceps. Thesurface of the tissue culture dish that is exposed by the removal of thecylinder is covered with molten agarose. This seals the bottom of thewell and provides a cell abhesive surface at the base of the well. Whenthe newly added molten LT agarose cools and solidifies, the resultingpre-shaped well is suitable for culturing, and stimulating theredifferentiation of proliferated chondrogenic cells. It is appreciated,however, that alternative methods may be used to prepare a pre-shapedwell useful in the practice of the invention.

B. Growth of Cartilage Patch

Proliferated chondrogenic cells in suspension (from section III A,hereinabove) subsequently are seeded into and cultured in the pre-shapedwell. The cells are diluted by the addition of cell culture medium to acell density of about 1×10⁵ -1×10⁹ proliferated chondrogenic cells perml, or more preferably about 1×10⁶ -5×10⁸ cells per ml, and mostpreferably about 3×10⁶ -2×10⁸ cells per ml. A preferred cell culturemedium comprises DMEM supplemented with 10% FBS. Alternatively, a cellculture medium comprising a 1:1 (vol/vol) mixture of Medium 199 and MCDB202, respectively, supplemented with 10% FBS may be used. Still anothercell culture medium useful in the practice of the invention comprises a3:1 (vol/vol) mixture of DMEM and F12, respectively, supplemented with10% FBS.

About, 1×10³ -1×10⁷ cells, preferably 1×10⁴ -1×10⁶ cells, and mostpreferably about 5×10⁴ -5×10⁵ cells produce a piece of syntheticcartilage 1 mm³ in volume. Accordingly, the artisan may produce a patchof synthetic cartilage of pre-determined size by seeding an appropriatenumber of chondrogenic cells into a pre-shaped well. The cellssubsequently are cultured at 37° C., 5% CO₂, for 1 to 90 days,preferably 5 to 60 days, and most preferably 10 to 30 days in order topermit secretion of cartilage-specific type II collagen and sulfatedproteoglycans thereby to form of synthetic cartilage in vitro. The cellculture medium is removed from the well and replaced with fresh cellculture medium every other day in order to maintain optimal viability ofthe cells.

Within about four hours of seeding the proliferated chondrogenic cellsinto the well, the cells coalesce to form a cohesive plug of cells. Thecells in the cohesive plug initially secrete type I collagen. Afterabout 4-10 days, the cells start to secrete cartilage-specific sulfatedproteoglycans and type II collagen. Over the same period of time, thelevel of type I collagen synthesis decreases. After prolonged periods oftime in culture the collagen expressed by the chondrogenic cells in thewell is predominantly type II collagen. It is contemplated however, thatthe cohesive plug of cells formed within four hours may be removed fromthe well and surgically implanted into the cartilage defect. It isanticipated that the undifferentiated chondrogenic cells subsequentlymay redifferentiate in situ thereby to form synthetic cartilage withinthe joint.

The resulting synthetic cartilage tissue formed in the pre-shaped wellmay be assayed, biochemically or morphologically, using the proceduresdescribed hereinabove prior to implantation into the joint. Briefly, thesynthetic cartilage may be sectioned into 8-18 μm sections using acryo-microtome (American Optical) and resulting sections stained usingthe procedures described in section III B.

It is contemplated that polypeptide growth factors may be added to thechondrogenic cells in the pre-shaped well to enhance or stimulate theproduction of articular cartilage specific proteoglycans and/or collagen(Luyten & Reddi (1992) in "Biological Regulation of the Chondrocytes",CRC Press, Boca Raton, Ann Arbor, London, and Tokyo, p.p. 227-236).Preferred growth factors include, but are not limited to transforminggrowth factor-β (TGF-β), insulin-like growth factor (IGF), plateletderived growth factor (PDGF), epidermal growth factor (EGF), acidicfibroblast growth factor (aFBF), basic fibroblast growth factor (bFBF),hepatocytic growth factor, (HGF) keratinocyte growth factor (KGF), thebone morphogenic factors (BMPs) i.e., BMP-1, BMP-2, BMP-3, BMP-4, BMP-5and BMP-6 and the osteogenic proteins (OPs), i.e. OP-1, OP-2 and OP-3.Preferred concentrations of TGF-β, IGF, PDGF, EGF, aFBF, bFBF, HGF, andKGF, range from about 1 to 100 ng/ml, more preferably from about 5 toabout 50 ng/ml, and most preferably from about 10 to about 20 ng/ml.Preferred concentrations of the BMP's and OP's range from about 1 toabout 500 ng/ml, more preferably from about 50 to about 300 ng/ml, andmost preferably from about 100 to about 200 ng/ml. However, theseparticular growth factors are not limiting. Any polypeptide growthfactor capable of stimulating or inducing the production of cartilagespecific proteoglycans and collagen may be useful in the practice of theinstant invention.

In addition, it is contemplated that ascorbate may be added to thechondrogenic cells in the pre-shaped well to enhance or stimulate theproduction of cartilage specific proteoglycans and collagen. Preferredconcentrations of ascorbate range from about 1 to about 1000 μg/ml, morepreferably from about 20 to about 500 μg/ml, and most preferably fromabout 50 to about 100 μg/ml.

V. Surgical Repair of Articular cartilage Defect Cartilage defects inmammals are readily identifiable visually during arthroscopicexamination or during open surgery of the joint. Cartilage defects mayalso be identified inferentially by using computer aided tomography (CATscanning), X-ray examination, magnetic resonance imaging (MRI), analysisof synovial fluid or serum markers or by any other procedures known inthe art. Treatment of the defects can be effected during an arthroscopicor open surgical procedure using the methods and compositions disclosedherein.

Accordingly, once the defect has been identified, the defect may betreated by the following steps of (1) surgically implanting at thepre-determined site, a piece of synthetic articular cartilage preparedby the methodologies described herein, and (2) permitting the syntheticarticular cartilage to integrate into pre-determined site.

The synthetic cartilage patch optimally has a size and shape such thatwhen the patch is implanted into the defect, the edges of the implantedtissue contact directly the edges of the defect. In addition, thesynthetic cartilage patch may be fixed in placed during the surgicalprocedure. This can be effected by surgically fixing the patch into thedefect with biodegradable sutures, i.e., (Ethicon, Johnson & Johnson)and/or by applying a bioadhesive to the region interfacing the patch andthe defect. Preferred bioadhesives include, but are not limited to:fibrin-thrombin glues similar to those disclosed in Fr. Pat. No. 2 448900; Fr. Pat. No. 2 448 901 and EP.S.N. 88401961.3 and syntheticbioadhesives similar to those disclosed in U.S. Pat. No. 5,197,973. Itis contemplated, however, that alternative types of sutures andbiocompatible glues may be useful in the practice of the invention.

In some instances, damaged articular cartilage maybe surgically excisedprior the to implantation of the patch of synthetic cartilage.Additionally, the adhesion of the synthetic cartilage patch to thearticular cartilage defect may be enhanced by treating the defect withtransglutaminase (Ichinose et al. (1990) J. Biol. Chem.265(3):13411-13414; Najjar et al. (1984) in "Transglutaminases", Boston,Martinuse-Nijhoff). Initially, the cartilage defect is dried, forexample by using cottonoid, and filled with a solution oftransglutaminase. The solution is subsequently removed, for example, byaspiration, leaving a film containing transglutaminase upon thecartilage. The synthetic cartilage patch is implanted subsequently intothe defect by the methods described above.

The synthetic cartilage patches preferably are allogeneic, and mostpreferably autogenic nature. Accordingly, synthetic allogeneic cartilagemay be prepared from biopsy tissue isolated from a mammal belonging tothe same species as the intended recipient. Synthetic autogeniccartilage may be prepared from biopsy tissue derived from the intendedrecipient.

In addition the synthetic cartilage may be useful in the repair of humanarticular cartilage defects. Accordingly, chondrogenic cells may beisolated from: human cartilage tissue, i.e, human articular cartilage(from weight-bearing and non-weight bearing joints), human costalcartilage, human nasal cartilage, human auricular cartilage, humantracheal cartilage, human epiglottic cartilage, human thyroid cartilage,human arytenoid cartilage and human cricoid cartilage; from humanperichondrial tissue, i.e., perichondrial tissue sampled from thesurface of human costal cartilage, human nasal cartilage, humanauricular cartilage, human tracheal cartilage, human epiglotticcartilage, human thyroid cartilage, human arytenoid cartilage and humancricoid cartilage; or from human bone marrow.

Surgical procedures for effecting the repair of articular cartilagedefects are well known in the art. See for example: Luyten & Reddi(1992) in "Biological Regulation of the Chondrocytes", CRC Press, BocaRaton, Ann Arbor, London, & Tokyo, p.p. 227-236, the disclosure of whichis incorporated by reference herein.

EXAMPLE I Isolation and Expansion of Chondrogenic Cells fromPerichondrial and Cartilage Tissue

Samples of human perichondrial tissue (HPT) and dog perichondrial tissue(DPT) were obtained from the Department of Orthopedic Surgery at Brighamand Women's Hospital, Boston, Mass. Samples of human articular cartilage(HAC) and dog articular cartilage (DAC) were obtained from theDepartment of Orthopedic Surgery at Brigham and Women's Hospital,Boston, Mass. and from the Department of Pathology, MassachusettsGeneral Hospital, Boston, Mass.

The tissues were minced finely and incubated overnight in a buffersolution containing 0.1% collagenase at 37° C., with agitation.Following the overnight digestion, the residual pieces of tissue wereharvested, and digested further with a solution containing 0.25%collagenase and 0.05% trypsin for 2-4 hours 37° C. The collagenase,trypsin step was repeated for a total of three times and the fractionscontaining denuded chondrogenic cells combined, and plated out into acell culture plate at a density of about 1×10³ -1×10⁴ cells per cm² ofthe plate.

The cells were cultured at 37° C., 5% CO₂ in a medium containing DMEMsupplemented with 10% FBS. When the cellular monolayers becameconfluent, the cells were washed three times with PBS and removed fromthe surface of the plate by adding a solution containing 0.05% trypsinto the monolayer. The trypsin was inactivated by the addition of 10% FBSto the suspension of cells. The number of cells in the single cellsuspension were counted, re-plated, proliferated and repassaged untiluse.

The proliferated chondrogenic cells were shown to maintain theirchondrogenic potential by culturing them in semi-solid agarose medium(Benya et al. (1982), supra). The proliferated cells were seeded into 2%LT agarose at a cell density of about 1×10³ -1×10⁶ cells per ml ofliquid agarose. Then, the cells were cultured at 37° C. for 21-35 days,as specified below, in a medium containing DMEM and 10% FBS. Thecolonies gave the appearance of small "nodules" in agarose. The controlswere chondrogenic cells that were grown as monolayers but not culturedin agarose culture.

The composition of the resulting particles was assayed by histochemicalstaining. The resulting particles were first fixed with 10% formalin inPBS. The cellular morphology and tissue phenotype was assessed bystaining a section of the agarose gel with hematoxylin/eosin. Thepresence of sulfated proteoglycans in the extracellular matrix wasassayed by staining the particles with 1% alcian blue in hydrochloricacid.

The presence of type I and type II collagen in the particles was assayedimmunohistochemically using the: anti-type I collagen monoclonalantibodies AB745 and MAB1340; and the anti-type II collagen monoclonalantibodies PS48 and CIICI in combination with the VECTASTAIN ABC-APimmunodetection kit (Vector Laboratory).

The results of the morphological and histochemical assays are summarizedin TABLE I, below. The presence and absence of type I collagen, type IIcollagen, and sulfated proteoglycans are represented by + and -,respectively.

                  TABLE I                                                         ______________________________________                                        Source of                                                                     Chondrogenic                                                                             Type I      Sulfated  Type II                                      Cells      Collagen    Proteoglycan                                                                            Collagen                                     ______________________________________                                        DPT                                                                           21 days    +           +         -                                            35 days    +           +         +                                            HAC                                                                           21 days    +           +         +                                            DAC                                                                           21 days    +           +         +                                            HAC                                                                           (monolayer)                                                                              +           -         -                                            DAC                                                                           (monolayer)                                                                              +           -         -                                            ______________________________________                                    

The results show that chondrogenic cells can be isolated from mammalianperichondrial tissue and cartilage. The cells also maintain theirchondrogenic potential following proliferation as monolayers.

EXAMPLE II Preparation of a Pre-shaped Well Having a Cell Contacting,Cell Abhesive Surface

It is appreciated that the size of the well may be dependent upon thesize of the piece of cartilage required. The wells prepared herein wereformed in LT agarose. 2 ml of a hot 2% agarose solution (not containingany cells) was poured into a tissue culture dish (35 mm in diameter)having a cylinder (3-5 mm, outside diameter) resting in the center ofthe dish. After the agarose solidified around the cloning cylinder (5-10minutes), the cylinder was carefully removed with forceps. The exposedsurface of the tissue culture dish resulting from the removal of thecloning cylinder was completely covered by the addition of a further50-100 μl of hot, liquid 2% agarose.

EXAMPLE III Preparation of Synthetic Articular Cartilage Patches InVitro

Another batch of proliferated chondrogenic cells prepared in accordancewith Example I were subsequently seeded as replicate samples into wellsprepared as described in Example II. The cells were either passagedtwice (2°) or three times (3°), as specified below, prior to seedingthem into agarose wells. Approximately, 1×10⁶ proliferated chondrogeniccells were seeded into the pre-shaped wells. The cells were cultured for14 days at 37° C., 5% CO₂ in growth medium containing DMEM supplementedwith 10% FBS.

The cells seeded into the agarose well were unable to attach to thesurface of the well. The chondrogenic cells, deprived of anchorage,interacted with one another and coalesced within about four hours togenerate a cohesive plug of cells. The chondrogenic cells began todifferentiate, as judged by the production of articular cartilagespecific markers. After 14 days in culture, the cohesive plugs of cellswere assayed morphologically and histochemically. The controls werechondrogenic cells that were grown as monolayers but not cultured in thepre-shaped wells.

The resulting patches and cellular monolayers were first fixed with 10%formalin in PBS. The cellular morphology and tissue phenotype wereassessed by staining a section of the patch with hematoxylin/eosin. Thepresence of sulfated proteoglycans in the extracellular matrix wasassayed by staining the remaining sections of the patches with either 1%alcian blue in hydrochloric acid or 0.2% safranin O/fast green.

The presence of type I and type II collagen in the particles was assayedimmunohistochemically using the: anti-type I collagen monoclonalantibodies AB745 and MAB1340; and the anti-type II collagen monoclonalantibodies PS48 and CIICI in combination with the VECTASTAIN ABC-APimmunodetection kit (Vector Laboratory).

The results of the morphological and histochemical assays are summarizedin TABLE II, below. The presence and absence of type I collagen, type IIcollagen, and sulfated proteoglycans are represented by + and -,respectively.

                  TABLE II                                                        ______________________________________                                        Source of                                                                     Chondrogenic Type I     Sulfated  Type II                                     Cells        Collagen   Proteoglycan                                                                            Collagen                                    ______________________________________                                        HPT (2°)                                                                            +          +         +                                           DPT (2°)                                                                            +          +         +                                           DAC (3°)                                                                            +          +         +                                           HAC (monolayer)                                                                            +          -         -                                           DAC (monolayer)                                                                            +          -         -                                           ______________________________________                                    

The results in TABLE II show that synthetic articular cartilage can beformed in vitro using chondrogenic cells that have been proliferatedpreviously in an undifferentiated state as cellular monolayers.

EXAMPLE IV Preparation of Synthetic Articular Cartilage Patches ofPre-determined Volume

Different numbers of chondrogenic cells derived from human and dogarticular cartilage and from human perichondrial tissue cartilage asprepared in Example I were seeded into pre-shaped wells as prepared inExample II. The cells were cultured for four days at 37° C., 5% CO₂ ingrowth medium containing DMEM supplemented with 10% FBS.

After 4 days in culture the patches were removed from the wells and thethickness and volume of the patches determined. The results aresummarized below in TABLE III.

                  TABLE III                                                       ______________________________________                                        (A) Chondrogenic Cells From Human Articular Cartilage                         Cell Number                                                                            Diameter of patch (mm)                                                                       Volume of patch (mm.sup.3)                            ______________________________________                                        a) 1 × 10.sup.5                                                                  1.0            0.8                                                   b) 5 × 10.sup.5                                                                  2.0            3.1                                                   c) 1.5 × 10.sup.6                                                                2.5            4.9                                                   (B) Chondrogenic Cells From Dog Articular Cartilage                           a) 1 × 10.sup.5                                                                  0.5            0.2                                                   b) 5 × 10.sup.5                                                                  1.0            0.8                                                   c) 1.5 × 10.sup.6                                                                2.0            3.1                                                   d) 5 × 10.sup.6                                                                  3.0            7.1                                                   (C) Chondrogenic Cells From Dog Perichondrial Tissue                          a) 1 × 10.sup.5                                                                  0.5 mm         0.2                                                   b) 5 × 10.sup.5                                                                  1.0 mm         0.8                                                   c) 5 × 10.sup.6                                                                  2.5 mm         4.9                                                   ______________________________________                                    

The results in Table III demonstrate that the volume of the resultingcartilage patches can be experimentally controlled by adjusting thenumber of cells seeded into the pre-shaped well.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiments are therefore to be considered illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than by the foregoing description, and all changes whichcome within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

What is claimed is:
 1. A method for repairing an articular cartilagedefect at a pre-determined site in a mammal, the method comprising thesteps of:(a) surgically implanting at the predetermined site of saiddefect a piece of synthetic cartilage of a predetermined volume preparedby the method comprising:(i) seeding denuded chondrogenic cells,proliferated ex vivo, into a preshaped well having a cell contacting,cell abhesive surface, said well being dimensioned to provide apredetermined volume of the synthetic cartilage so that said volumeapproximates a volume of the cartilage defect to be repaired; (ii)culturing said cells in said well for a time sufficient to permit saidcells to differentiate and form a synthetic cartilage comprisingchondrogenic cells dispersed within an endogenously producedextracellular matrix; (iii) removing said synthetic cartilage from saidwell; and (b) permitting the synthetic cartilage to integrate into thepredetermined site.
 2. The method of claim 1, comprising an additionalstep of fixing said synthetic cartilage at said pre-determined site. 3.The method of claim 2, wherein said additional step comprises surgicallyfixing said synthetic cartilage at said pre-determined site.
 4. Themethod of claim 2, wherein said additional step comprises applying abioadhesive to the interface of said pre-determined site and saidsynthetic cartilage.
 5. The method of claim 1, wherein said methodcomprises the additional step of excising defective articular cartilagefrom said site prior to implanting the synthetic cartilage.
 6. Themethod of claim 1, wherein step (a) is effected by implanting aplurality of synthetic cartilage pieces at said site.
 7. The method ofclaim 1, wherein said defect is a partial thickness defect.
 8. Themethod of claim 1, wherein said synthetic cartilage is autogenic orallogeneic.
 9. A method for repairing an articular cartilage defect at apre-determined site in a mammal, the method comprising the steps of:(a)surgically implanting at the predetermined site of said defect a pieceof synthetic cartilage of a pre-determined volume prepared by the methodcomprising:(i) providing a tissue comprising interconnected chondrogeniccells; (ii) disaggregating said tissue to release denuded cells; (iii)proliferating said denuded cells ex vivo; (iv) seeding said proliferatedcells into a preshaped well having a cell contacting, cell abhesivesurface, said well being dismensioned to provide a predetermined volumeof the synthetic cartilage so that said volume approximates a volume ofthe cartilage defect to be repaired; (v) culturing said cells in saidwell for a time sufficient to permit said cells to differentiate andform a formation of synthetic cartilage comprising chondrogenic cellsdispersed within an endogenously produced extracellular matrix; (vi)removing said synthetic cartilage from said well; and (b) permitting thesynthetic cartilage to integrate into the pre-determined site.
 10. Amethod for repairing an articular cartilage defect at a predeterminedsite in a mammal, the method comprising the steps of:(a) surgicallyimplanting at the predetermined site of said defect a piece of syntheticcartilage of a pre-determined volume prepared by the methodcomprising:(i) seeding denuded chondrogenic cells, proliferated ex vivo,into a preshaped well having a cell contacting, cell abhesive surface,said well being dimensioned to provide a pre-determined volume of thesynthetic cartilage so that said volume approximates a volume of thecartilage defect to be repaired; (ii) adding ascorbate to said cells insaid well; (iii) culturing said cells in said well for a time sufficientto permit said cells to differentiate and form a synthetic cartilagecomprising chondrogenic cells dispersed within an endogenously producedextracellular matrix; (iv) removing said synthetic cartilage from saidwell; and (b) permitting the synthetic cartilage to integrate into thepredetermimined site.
 11. The method of claims 1, 9 or 10, wherein saidcell abhesive surface comprises a surface coated with silicon orpolytetrafluoroethylene.
 12. The method of claims 1, 9 or 10, whereinsaid well is defined by a material selected from the group consisting ofagarose, glass, untreated cell culture plastic andpolytetrafluoroethylene.
 13. The method of claims 1, 9 or 10, whereinsaid chondrogenic cells are derived from cartilage.
 14. The method ofclaims 1, 9 or 10, further comprising an additional step of adding apolypeptide growth factor selected from the group consisting oftransforming growth factor -β, platelet derived growth factor,insulin-like growth factor, acidic fibroblast growth factor, basicfibroblast growth factor, epidermal growth factor, hepatocytic growthfactor, keratinocyte growth factor, and bone morphogenic protein to thecells prepared by the method in step (a).
 15. A method for repairing anarticular cartilage defect at a pre-determined site in a mammal, themethod comprising the steps of:(a) surgically implanting at thepredetermined site of said defect a piece of synthetic cartilage of apredetermined volume prepared by the method consisting of:(i) seedingdenuded chondrogenic cells, proliferated ex vivo, into a preshaped wellhaving a cell contacting, cell abhesive surface, said well beingdimensioned to provide a predetermined volume of the synthetic cartilageso that said volume approximates a volume of the cartilage defect to berepaired; (ii) culturing said cells in said well for a time sufficientto permit said cells to differentiate and form a synthetic cartilageconsisting of chondrogenic cells dispersed within an endogenouslyproduced extracellular matrix; (iii) removing said synthetic cartilagefrom said well; and (b) permitting the synthetic cartilage to integrateinto the predetermined site.